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  1. #51
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    Click here to enlarge Originally Posted by AltecBX Click here to enlarge
    I need to understand this in laymen's term.

    By running a lower resistor (1k) than a (4.7k), you are able to reach better AFR targets at boost greater +16psi?
    If both tunes are targeting 19 psi, one with 1k & the other with 4.7k, will the 4.7k save more fuel and still achieve the same boost level?
    To run nitrous, is the 4.7k not good enough to run safely?
    If having a 1k resistor in there and the advantage of it's running richer AFR and then have it run leaner for less boost, why not then have it adjustable through the user menu on the desire boost target selected?
    Are JB3 cars making more power because they run richer lambda?
    Quoted as this is something Shiv needs to keep in mind.
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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Quoted as this is something Shiv needs to keep in mind.
    By biasing the resistor, you are making the DME think it is running leaner than it is. The lower value resistor you use, the leaner the DME interprets the AFR. By biasing a 0v signal with a 1k resistor, the DME assumes it is running a not-plausible lambda value. Also, heavily biasing the wideband also has an unknown effect on o2 sensor longevity as well as a loss in fuel targeting granularity on the tuning side. Been there, done that. It's amusing that 4 years after we design this wideband biasing circuitry, that copy-cats are just now realizing that different resistors have different effects. But with no concern beyond the obvious things they see through basic dyno/afr logging.

    Sticky- carefully read my previous post as it explains the effects (or lack thereof) of over-fueling a DI engine.

    Shiv

  3. #53
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    Click here to enlarge Originally Posted by shiv@vishnu Click here to enlarge
    By biasing the resistor, you are making the DME think it is running leaner than it is. The lower value resistor you use, the leaner the DME interprets the AFR. By biasing a 0v signal with a 1k resistor, the DME assumes it is running a not-plausible lambda value. Also, heavily biasing the wideband also has an unknown effect on o2 sensor longevity as well as a loss in fuel targeting granularity on the tuning side. Been there, done that. It's amusing that 4 years after we design this wideband biasing circuitry, that copy-cats are just now realizing that different resistors have different effects. But with no concern beyond the obvious things they see through basic dyno/afr logging.

    Sticky- carefully read my previous post as it explains the effects (or lack thereof) of over-fueling a DI engine.

    Shiv
    I should have been more specific, I was not questioning your explanation but reminding you of just the wide spectrum of people reading this:

    Click here to enlarge Originally Posted by AltecBX
    I need to understand this in laymen's term.
    Sometimes you forget everyone is not a tuner.

    And yes, you can't treat a DI motor like a port injection motor.
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  4. #54
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    Click here to enlarge Originally Posted by shiv@vishnu Click here to enlarge
    Incorrect. And it doesn't look like you even understand the relationship between EGT and ignition advance. The less advance, the higher the EGT due to decrease in combustion efficiency. Not the other way around. What I was getting at is that running a 11:1 AFR at peak torque has no EGT-reduction effect compared to running 13:1. Nor does it have any effect on knock resistance. It's only until you enlean AFR above 15:5 at, or around, peak torque, does knock resistance take a measurable turn for the worse. No surprise that BMW tunes for a Lambda of ~1.1 (16.2:1 AFR) at peak torque, albeit at lower boost pressures.
    I said controlling EGT but meant controlling detonation. I understand under-advancing allows more fuel to burn in to the exhaust stroke increasing EGT. But the air/fuel effects on EGT and knock resistance are undeniable even in DI applications. And it's not simply about midrange air/fuel ratios. The smaller resistors allow richer air/fuel ratios up top also. And I'm not sure what this 0v business is. I would not suggest sitting on 0v w/ 1k resistors. You need to set the curve properly. You also need to ensure the tune is switching to a voltage other than 2.25v during the oxygen sensor calibrations. Something I'm not convinced the PROcede is doing properly...
    Last edited by Terry@BMS; 07-06-2010 at 06:16 PM.

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    Click here to enlarge Originally Posted by shiv@vishnu Click here to enlarge
    By biasing the resistor, you are making the DME think it is running leaner than it is. The lower value resistor you use, the leaner the DME interprets the AFR. By biasing a 0v signal with a 1k resistor, the DME assumes it is running a not-plausible lambda value. Also, heavily biasing the wideband also has an unknown effect on o2 sensor longevity as well as a loss in fuel targeting granularity on the tuning side.

    Shiv
    I am curious, is this speculation or fact? Can someone prove that biasing the O2 sensors will cause them to prematurely fail?




    Click here to enlarge Originally Posted by shiv@vishnu Click here to enlarge
    By biasing the resistor, you are making the DME think it is running leaner than it is. The lower value resistor you use, the leaner the DME interprets the AFR. By biasing a 0v signal with a 1k resistor, the DME assumes it is running a not-plausible lambda value. Also, heavily biasing the wideband also has an unknown effect on o2 sensor longevity as well as a loss in fuel targeting granularity on the tuning side. Been there, done that. It's amusing that 4 years after we design this wideband biasing circuitry, that copy-cats are just now realizing that different resistors have different effects. But with no concern beyond the obvious things they see through basic dyno/afr logging.

    Sticky- carefully read my previous post as it explains the effects (or lack thereof) of over-fueling a DI engine.

    Shiv
    So what exactly are these things you're talking about 'beyond' the dyno and AFR? Isn't that the whole point of running more boost? Stay safe by going rich?

    I am just wondering what else there is to it since you claimed there are adverse affects, what are they?
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  6. #56
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    Click here to enlarge Originally Posted by DBFIU Click here to enlarge
    I am curious, is this speculation or fact? Can someone prove that biasing the O2 sensors will cause them to prematurely fail?
    I can't think of any theoretical relationship between current biasing and sensor longevity. But if one existed it would exist at .5ma (5k) as well. IIRC biasing is actually reducing the current through the sensor. In practice we've been doing the 3.3ks for race boards for over a year (maybe 100 out there?) without a single reported related issue. Doing long term 1k testing now. But so far so good. It's more complicated than just throwing 5k resistors on and setting voltage to 0 like we used to do with the JB2 but no pain no gain. And the tuning benefits make it worth the extra programming time IMHO.

    Also you'll note Shiv mentions the higher RPM (peak power) benefits of a richer air/fuel ratio. I'll again refer you to this 5k vs. 1k comparison dyno.

    Click here to enlarge

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    Click here to enlarge Originally Posted by shiv@vishnu Click here to enlarge
    Incorrect. And it doesn't look like you even understand the relationship between EGT and ignition advance. The less advance, the higher the EGT due to decrease in combustion efficiency. Not the other way around. What I was getting at is that running a 11:1 AFR at peak torque has no EGT-reduction effect compared to running 13:1. Nor does it have any effect on knock resistance. It's only until you enlean AFR above 15:5 at, or around, peak torque, does knock resistance take a measurable turn for the worse. No surprise that BMW tunes for a Lambda of ~1.1 (16.2:1 AFR) at peak torque, albeit at lower boost pressures.

    At higher engine speed, requirements change a bit in that the DI effects are diminished. I suspect this has to do with combustion events having less time between them, which doesn't allow for proper air/fuel stratification. Which means excess fuel must be introduced into the cylinder to ensure a complete burn while maximum charge expansion at the time in the combustion cycle.



    I'd be interested to know why your findings, if they do in fact exist, deviate from mine. As wel as basic engine theory with regards to Direct Injection and it's effects/benefits.

    Shiv

    PS. I'm looking forward to Lost Marine given me a negative Rep again.
    just keep posting, i just want to hear your side of things, for that i will not neg, BS def gets it though. i should neg for bringing up my name in an irrelevent conversation, but i digress. Click here to enlarge

  8. #58
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    Click here to enlarge Originally Posted by Terry@BMS Click here to enlarge
    No amount of instant timing retard is going to prevent it. What is required is more octane, more fuel, less boost, less overall advance, colder plugs, etc.
    That's what I just said. LESS OVERALL advance upfront proactively. Out of all those things you had listed, the most crucial to EGT's and overall cylinder pressure is advance, have you tested what + or - 1 or 2 degrees can actually do to those EGT? A bandaid of overfueling won't fit this.
    Last edited by BrenM3; 07-07-2010 at 12:43 AM.

  9. #59
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    Click here to enlarge Originally Posted by BrenM3 Click here to enlarge
    That's what I just said. LESS OVERALL advance upfront. Out of all those things you had listed, the most crucial to EGT's and overall cylinder pressure is advance, have you tested what 1 or 2 degrees can actually do to those EGT? Not wash out by overfueling a DI motor.
    I think we're confusing a few things. Detonation is actually a great way to reduce your EGTs. But has other more serious drawbacks. Click here to enlarge

    I'd gamble to say we will all agree the advance has to be right for a given boost, temperature, octane, etc. Too far advanced and you'll detonate, too far back and EGTs will increase, both at the expense of power. What we'll probably disagree on is whether using an advance limiter in the N54 is an effective means of timing control given the limitations I've outlined before. We'll also disagree on best practices when pushing things to the edge. e.g. assuming timing will float up to 15 given the right conditions and setting boost, octane, etc with that in mind.

    But this discussion is really about air/fuel ratios and their effect on knock resistance and EGT reduction. And ultimately about reducing preignition.
    Last edited by Terry@BMS; 07-07-2010 at 12:58 AM.

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    So why doesn't someone state the dangers of over-fueling a DI motor just to provide the other perspective?
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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    So why doesn't someone state the dangers of over-fueling a DI motor just to provide the other perspective?
    Curious with this as well. I don't see what the drawback could be trying to attain lower than normal AFRs (11:1, 10:1 etc...) like you would with a port injected engine.

    If anything it would help control detonation. Correct?
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  12. #62
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    would be interesting to know that as well...as far as I know DI setups run leaner in general than port injection ones but how that needs to change with respect to higher boost/fuel especially on stock ign advance curves I have no idea...

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    I would imagine the same rules apply, once the intake valve is closed and the air/fuel mixture is in the cylinder; the engine has X and Y amount of chemical reagents and didnt care how it got there. Pre-ignition can still occur, which is why going richer whether DI or not makes sense to me. Pre-igniting takes place after the intake valve is closed correct? So what's the difference going rich in DI or port inject?

    Please shed light on this, thanks.
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    It looks like we've discussed the topic a bit before. This exchange is from March, 2007, when the procede v1 had been out for a couple months and I was new to the scene.

    Click here to enlarge Originally Posted by Terry Burger
    I don't see how the car is running 14-15:1 AF ratios under boost, but I guess BMW knows something I don't.
    ...


    Click here to enlarge Originally Posted by shiv@vishnu
    It only runs that AFR in the low to midrange for maximum on boost fuel economy and emissions since EGT isn't too much of a concern at those engine speeds. Up top, it richens up to 13:1 which is lean by conventional standards. Then again, the stock engine is only make 100hp/liter (something that many modern engines come close to making without turbochargers) so it can get away with such stingy fuel mapping. Early in our xede development, we were at a point where we only had control over boost and timing and we found that the car was very inconstant and ping prone with the factory fuel mapping when asked to run higher boost (not exactly surprising).
    ...

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    Click here to enlarge Originally Posted by DBFIU Click here to enlarge
    I would imagine the same rules apply, once the intake valve is closed and the air/fuel mixture is in the cylinder; the engine has X and Y amount of chemical reagents and didnt care how it got there. Pre-ignition can still occur, which is why going richer whether DI or not makes sense to me. Pre-igniting takes place after the intake valve is closed correct? So what's the difference going rich in DI or port inject?

    Please shed light on this, thanks.
    Good question.
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    Is there an inconsistency in Shiv's inputs? He said richer is needed in the beginning of the thread as well as a few years back, and that he can still do it with his fixed resistors. However, the data does not support he can do it with those resistors, and now he says it is not good to run rich as it might be "too rich".

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    Click here to enlarge Originally Posted by 654 Click here to enlarge
    Is there an inconsistency in Shiv's inputs? He said richer is needed in the beginning of the thread as well as a few years back, and that he can still do it with his fixed resistors. However, the data does not support he can do it with those resistors, and now he says it is not good to run rich as it might be "too rich".
    That post from earlier does seem to bring about a bit of an inconsistency but then again N54 tuning and our understanding has evolved since that time.
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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    That post from earlier does seem to bring about a bit of an inconsistency but then again N54 tuning and our understanding has evolved since that time.
    which is why we need to hear from both sides

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    Click here to enlarge Originally Posted by 654 Click here to enlarge
    Is there an inconsistency in Shiv's inputs? He said richer is needed in the beginning of the thread as well as a few years back, and that he can still do it with his fixed resistors. However, the data does not support he can do it with those resistors, and now he says it is not good to run rich as it might be "too rich".
    I agree. The proper solution is for him to offer to change them for customers who require richer/air fuel ratios. Then the customer can decide in the software interface how rich they want to go.

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    Click here to enlarge Originally Posted by Terry@BMS Click here to enlarge
    I agree. The proper solution is for him to offer to change them for customers who require richer/air fuel ratios. Then the customer can decide in the software interface how rich they want to go.
    I thought the Autotune decides for you?
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    2 out of 2 members liked this post. Yes Reputation No
    I am overwhelmed with all this volt and resistor stuff. It sounds like Terry knows more about engineering than tuning. Is it just me?

    And, why would it be bad if what Shiv did and said in V1 is different than in V3. Like Sticky said, a lot of things have been learned and discovered over time.

    I might sound like a Shiv fan, but honestly when Shiv writes and discusses issues about tuning, it makes a lot more sense to me.

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    After reading this thread several times and really got confused about resistors etc I decided to comment on the basics instead.
    Terry makes a fundamental error of using tuning targets that are known for conventional injected motors. Another error he makes is that he keeps using flash tunes as reference by saying "a flash tune has this and that AFR's". Besides the fact that most flash tunes are pirated from one person or not it does not necessarily mean that the tune be it a flash or not is correct.
    This leads to a completely new discussion of Direct injection and AFR's. When comparing conventional injection and direct the most important aspect to consider is what occurs in the combustion chamber. There is a very big difference between the two and what comes out of the exhaust in terms of unspent fuel is not really a indication of what occurred in the combustion chamber. We can have a in depth conversation about this in another thread but basically the AFR a DI engine should have is relative to each manufacturers piston design and combustion engineering. I have found that with BMW you can run a far leaner AFR, always remembering that lean in the exhaust is not necessarily a lean combustion on the piston as it only indicates a average of the combustion that occurred over the piston. In terms of detonation and prevention we must also remember that the DI injects the fuel at a totally different period in the cycle to conventional. So basically we got to throw out all we knew and start fresh with out of the box thinking.

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    I haven't heard anyone suggest you should run 11:1 because they ran that with motor XYZ and it worked great.

    Historically N54 piggybacks have not been able to run richer air/fuel ratios. Limited by the hardware (resistors/software) and tuner detection codes. Only recently have both of those items been worked out to allow the piggyback full control over air/fuel.

    Personally, we started not by reworking the piggyback to allow much richer air/fuel ratios but by testing those ratios in our N54 using flash software. With the Dimsport setup you have a few simple 2D tables where you enter the lambda and the ECU targets it. You can enter whatever you want. .600 if you want. And during that tested we observed benefits when going richer (10.8-11.2:1) at higher boost levels on pump gas in regards to detonation resistance and EGT reduction.

    Then we turned to the piggyback side and configured it so we could target the same air/fuel ratios we could with the Dimsport setup. We can also set it much leaner if we want. The piggyback now has a much wider range of fuel control. And now that those ratios are available to end users I expect many will also find the benefits of going richer in this application.
    Last edited by Terry@BMS; 07-09-2010 at 11:17 AM.

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    Great info in this thread!

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    Click here to enlarge Originally Posted by George Smooth Click here to enlarge
    After reading this thread several times and really got confused about resistors etc I decided to comment on the basics instead.
    Terry makes a fundamental error of using tuning targets that are known for conventional injected motors. Another error he makes is that he keeps using flash tunes as reference by saying "a flash tune has this and that AFR's". Besides the fact that most flash tunes are pirated from one person or not it does not necessarily mean that the tune be it a flash or not is correct.
    This leads to a completely new discussion of Direct injection and AFR's. When comparing conventional injection and direct the most important aspect to consider is what occurs in the combustion chamber. There is a very big difference between the two and what comes out of the exhaust in terms of unspent fuel is not really a indication of what occurred in the combustion chamber. We can have a in depth conversation about this in another thread but basically the AFR a DI engine should have is relative to each manufacturers piston design and combustion engineering. I have found that with BMW you can run a far leaner AFR, always remembering that lean in the exhaust is not necessarily a lean combustion on the piston as it only indicates a average of the combustion that occurred over the piston. In terms of detonation and prevention we must also remember that the DI injects the fuel at a totally different period in the cycle to conventional. So basically we got to throw out all we knew and start fresh with out of the box thinking.
    Well said.

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